Co-assembled hole selective contact enables highly efficient organic solar cells and tandems

The self-assembled monolayer (SAM), functioning as a hole transport layer, holds the potential to substantially elevate the efficiency of perovskite and organic solar cells. Nevertheless, incomplete SAM coverage may result in interface defects lurking between the photovoltaic layer and the electrode, thereby causing non-radiative recombination losses of interfacial charges. To tackle this issue, we introduced 4-bromobutyric acid to co-assemble with the SAM, yielding a more compact co-assembled monolayer (co-SAM) that effectively repairs these defective zones. Confocal laser scanning microscopy and Kelvin Probe Force Microscopy show that co-SAMs successfully mitigate interface defects in the previously uncovered electrode regions. Furthermore, the work function of the electrodes is elevated to 5.6 eV, facilitating efficient hole extraction. Consequently, devices incorporating co-SAMs exhibit notably reduced non-radiative recombination losses. The power conversion efficiency (PCE) of the devices is enhanced to 20.0% in binary organic solar cells, and an even more remarkable breakthrough PCE of 25.8% is achieved in perovskite/organic tandem devices. This study introduces a straightforward strategy to improve the hole-selective contact of electrodes, ultimately boosting the overall efficiency of the devices.